SPY secrets whistleblower Edward Snowden has vanished after failing to catch the Cuban-bound flight he was due to leave Moscow on today.

Security around the aircraft at Sheremetyevo Airport was heavy prior to boarding and guards tried to prevent photographers and cameramen from taking pictures of the plane, heightening the speculation that he might have been secretly escorted on board.

But the Interfax news agency, which has extensive contacts with Russian security agencies, said he could have flown out in a different plane.

Russian airline Aeroflot said earlier that Mr Snowden had registered for the flight using his American passport, which the United States recently cancelled.

He has not been seen since he arrived in Moscow on Sunday from Hong Kong, where he had been hiding for several weeks to evade US justice. Ecuador is considering his asylum application.

After spending a night at Moscow' airport, the former National Security Agency contractor had been expected to fly to Cuba and Venezuela en route to possible asylum in Ecuador.

Mr Snowden, also a former CIA technician, fled Hong Kong to dodge US efforts to extradite him on espionage charges. Ecuador's Foreign Minister Ricardo Patino confirmed his government had received an asylum request, adding that the decision "has to do with freedom of expression and with the security of citizens around the world." The anti-secrecy group WikiLeaks also said it would help.

Ecuador has rejected the United States' previous efforts at cooperation, and has been helping WikiLeaks founder Julian Assange avoid prosecution by allowing him to stay at its embassy in London.

Mr Snowden gave documents to the media disclosing US surveillance programs that collect vast amounts of phone records and online data in the name of foreign intelligence, often sweeping up information on American citizens.

He had been in hiding for several weeks in Hong Kong. The United States formally sought his extradition to face espionage charges but was rebuffed; Hong Kong officials said the US request did not fully comply with their laws.

The United States was in touch through diplomatic and law enforcement channels with countries that Mr Snowden could travel through or to, reminding them he is wanted on criminal charges and reiterating Washington's position that he should only be permitted to travel back to the US.

But the United States is likely to have problems interrupting Mr Snowden's passage. It does not have an extradition treaty with Russia, but does with Cuba, Venezuela and Ecuador. Even with an extradition agreement though, any country could give him a political exemption.

The likelihood that any of these countries would stop himfrom traveling on to Ecuador seemed remote. While diplomatic tensions have thawed in recent years, Cuba and the United States are hardly allies after a half-century of distrust.